The purpose of this study was to determine the safety of a new casein hydrolysate formula, Formula X, for use in children with cow's milk allergy (CMA). Laboratory animal studies and physicochemical studies suggested CMA children would not react to Formula X. However, 2 of 4 CMA children experienced urticaria and milk abdominal symptoms after ingesting the formula in a double-blind trial. The clinical study was terminated and the formula is being reformulated.